This research is characterizing monocyte-macrophages by a combination of biological, histochemical and ultrastructural techniques. Methodology for assessment of the above parameters is being developed. Simultaneous utilization of these newer techniques in patients showing unusual susceptibility to infection is uncovering new syndromes of macrophage deficiency. New approaches to bone marrow transplantation utilizing total lymphoid irradiation are being perfected in experimental animals and heart transplant patients.